The present invention relates to a method using fumed silica as a hydrophobic sorbent material, particularly for the sorbing of hydrocarbons from the surface of water.
A serious problem which long has plagued industrial and environmental concerns is the removal of hydrocarbons, particularly oil, from unwanted areas into or onto which it has been discharged. Of particular concern is the removal of discharged oil from water or shore areas which occurs as a result, for example, of oil tanker accidents at sea or mishaps in the loading or unloading of oil from these tankers in port. Other occasions where hydrocarbon removal is of concern range from problems such as the discharge of oil at areas around oil wells and oil storage facilities or the cleaning of surfaces in which oil was stored (e.g. on-shore storage tanks, holds of tankers, etc.) to problems such as the discharge or leaking of oil from vehicles onto roads or driveway surfaces. Further, oil-water emulsions which are used, for example, as cutting fluids require separation of oil from the water prior to disposal.
Numerous solutions have been proposed for dealing with the problem of removing hydrocarbons from unwanted areas. One of these solutions involves the use of bacteria to degrade the hydrocarbons. However, such methods are expensive, raise important environmental concerns, and are often ineffective in cold weather environments.
Another solution to the problem lies in the use of absorbents which are intended to remove the hydrocarbons from unwanted areas by the use of physical forces rather than chemical break down of the hydrocarbons, i.e. where it is drawn into the absorbent material in much the same way water is drawn into a sponge.
Numerous examples of absorbents of this type are found in the literature. In U.S. Pat. No. 3,630,891 there is disclosed an oil absorbent prepared from wood fibers which have been treated with sizing material to render the fibers water repellant.
U.S. Pat. No. 3,770,575 discloses wet wood pulp treated with sizing and subjected to flash drying.
U.S. Pat. No. 3,382,170 discloses the use of perlite, a mineral containing silica, to absorb oil.
U.S. Pat. No. 3,591,524 discloses an oil absorbent comprised of cellulosic base impregnated with a complex oil-in-water, ammonium or amine-containing emulsion.
U.S. Pat. No. 3,756,948 discloses the use of polystyrene foam crumbs.
U.S. Pat. No. 4,131,543 discloses the use of insoluble silicate aggregates to absorb oil as well as other industrial solvents and acids.
U.S. Pat. No. 4,172,039 discloses the use of porous coconut husk material, such as coir dust, treated with an oleophilic-hydrophobic substance. The patent also discuss a method of absorption comprising the use of containers filled with the sorbent and which float on the surface of the water thereby absorbing the oil.
U.S. Pat. No. 4,343,680 discloses enhancing the oleophilic-hydrophobic properties of wood pulp by heating and fluffing.
U.S. Pat. No. 4,670,156 discloses the use of fibrous cellulosic material, e.g. sulphite reject, which is subjected to forced heating to enhance hydrophobic and oleophilic properties.
Some of the limitations of the examples mentioned above include prohibitive cost; ineffectiveness in extreme environmental conditions; tackiness of the material after it is saturated with oil; retention of oil in the absorbent until the absorbent is removed from the water; and ineffective or temporary hydrophobic characteristics.
In order to effectively remove hydrocarbons from water it is necessary that the absorbent absorb only the hydrocarbon and not the water. That is, the material should be both oleophilic and hydrophobic. Fine particulate silica has been known to exhibit both of these properties. See for example U.S. Pat. No. 4,054,689 which discloses silica treated with HF in order to make the silica hydrophobic without disturbing its oleophilic properties. The resultant material readily absorbs oil from the surface of water. However, upon standing in water for a number of hours, the silica loses its hydrophobicity, becomes hydrophilic, and enters the water, leaving the oil floating on top.
The aforementioned U.S. Pat. No. 3,382,170 discloses that the mineral "Perlite", which contains 65%-75% by weight SiO.sub.2, exhibits hydrophobic properties upon treatment with an emulsion of polydimethylsiloxane in water at 200.degree. C. to 500.degree. C.
U.S. Pat. No. 4,526,780 discloses the use of fumed silica as a suspending agent in a deodorant composition which aids in the absorption of silicone oils. However, it is also taught that fumed silicone alone will not yield a stable product because the oil separates out.
U.S. Pat. No. 4,708,997 discloses the treatment of hydrophilic silicon dioxide with polydimethyldichlorosilane in order to render the material hydrophobic. This material is then used as one part of a suspending agent in the water-in-oil suspension polymerization of water soluble monomers.
U.S. Pat. No. 4,191,677 discloses the use of "TULLANOX" fumed silica to prevent water absorption in a two-part epoxy adhesive system.
U.S. Pat. No. 4,536,399 discloses the use of fumed silica to absorb oil from skin.
Although no documentation has been found for support, it is understood that Cabot Corporation has experimented with hexamethyldisilazane (HMDZ) treated fumed silica for absorption of crude oil on sea water.
The problem with using amorphous silica, and in particular fumed silica, is that it is normally hydrophilic and oleophilic. A treatment process is needed in order to render the material hydrophobic, and these treatment process are not always permanent. That is, after a period of time after exposure to water the silica often reverts back to its original hydrophilic property.
Another problem is that after treated silica is exposed to and has absorbed the hydrocarbons, the material does not agglomerate. Thus, is is difficult, if not impossible, to recover the saturated material without the use of very fine mesh screens.
It is therefore an object of this invention to provide a method for absorbing hydrocarbons from water while not absorbing the water.
It is further an object of this invention to provide a method for recovering hydrocarbons from the surface of water by the use of an absorbent material that can remain in water indefinitely without losing its hydrophobicity.
It is further an object of this invention to provide a method for recovering hydrocarbons from the surface of water by the use of an absorbent material that can be easily recovered after becoming saturated with the hydrocarbons.
It is further an object of this invention to provide a method for recovering hydrocarbons from the surface of water by the use of an absorbent material that is both hydrophobic and oleophilic.
Other objects will become apparent to those skilled in the art upon reading the following.